68 AUSTRALIAN SKY & TELESCOPE April 2018
Gain and offset
Two unusual adjustable settings I hadn’t
encountered on previous cameras
arefor‘gain’and‘offset’.Gainis
usuallypermanentlysetbythecamera
manufacturer, and an offset is often
added during image calibration.
Sliders to adjust these settings are
accessed in theEZCAP_QTsoftware
supplied with the camera. The default
settings resulted in low sensitivity
in my initial tests, so after some
experimentation, I settled on settings of
10 for gain and an offset of 124.
Althoughthecameraandfilterwheel
can be fully operated using the supplied
EZCAP_QTsoftware, I preferred to
operate the camera and filter wheel
usingMaxIm DL.
UsingMaxIm DLto control the
QHY16200Arequiredinstalling
ASCOM Captureand the camera driver
I downloaded from the QHY website,
whichalsoprovidesadjustmentsettings
for gain and offset. Initially, the driver
didn’tallowthesoftwaretoconsistently
connecttothecamera.Anupdated
driverinstalledlaterduringmytesting
eliminated this problem.Under the stars
I used the QHYOAG-M off-axis guider
toautoguideallofmytestexposures
with the camera. Besides being a solid
unit, the guider features a moveablepick-off prism that can be adjusted
adially then securely locked into
position. I adjusted the pick-off prism’s
position so that it was well outside the
mage field of view so as not to cast its
hadow on the camera’s imaging area.
Guiding off axis also helps to
eliminate any flexure that might
arisefromguidingthroughaseparate
guidescopeduetotheweightofthe
camera. I never had an issue with
finding suitably bright guidestars
using the OAG with a Starlight Xpress
Lodestar X2 guide camera. The 1¼-inch
guide camera port has three locking
screws 120$apart. The guide camera is
focused by sliding it in and out of the
port, with a comfortable amount of
focus travel available.
The 7-position filter wheel
consistently placed each filter in the
correct position as I worked through a
typical LRGB imaging session. The filter
wheel was surprisingly quiet as each
filter rotated into place, with the only
indication of the moving wheel beingthe“waitingonfilterwheel”alertgiven
inMaxIm DLfor the few seconds that
thefilterwheelwasinmotion.After
months of using the camera and filter
wheel, there was not a single time when
the selected filter didn’t move into the
correct position. Each time I launched
the camera software, it knew which
filter was already in position.
As testament to the machining and
fit of the filter wheel, camera, and off-
axis guider components, the stack of all
three is effectively a light tight package.
This allowed me to make dark frames
during daylight with my observatory
dome closed, even though there was
still considerable ambient light inside
the dome.
Iusedthesoftware’s4×4binning
featuretocentreandcomposemy
deepskytargets,sincethebinning
greatly increased the camera sensitivity.
The two-stage cooler reached the set
temperature quickly and was stable to a
tenth of a degree C throughout my test
sessions. A full-resolution, 36-megabytep r p p i s e a g cfi
u
L
SThe 7-position QHYOAG filter wheel
accepts 50-mm filters (not included with
purchase). Tools are supplied with the unit to
allow easy access to the filter wheel housing
forinstallationofthefilters.SA custom-machined adapter was used
with the QHY16200A camera to enable better
illumination of the camera’s large chip when
used with the author’s 31.8-cm f/4 Newtonian
equipped with a Tele Vue Paracorr Type 2
coma corrector. The corrector threads into the
adapter, while male threads on the adapter’s
underside screw into the camera’s 54-mm
ring, producing a clear aperture of 50 mm.WTwo adapter rings are supplied with the
QHY16200A camera. The T-thread adapter is
shown here installed while the 54-mm adapter
is held in front. Both are secured to the filter
wheel housing by six M3 screws. The off-axis
guider’s pick-off prism is visible inside the
T-thread opening.AS&T TEST REPORT